1. Field of the Invention
The present invention relates generally to brake systems and more particularly to multi-disk brake systems and techniques for reducing vibrations which occur in such multi-disk brake systems during a braking event.
2. Description of the Related Art
A multi-disk brake system typically has a brake disk stack having alternate disks keyed to and rotatable with a wheel, while intervening disks are keyed to the stationary brake housing. Multi-disk brake systems are frequently used in aircraft. The non-rotating disks are supported by a torque tube which is fixed to the brake housing and extends in an outboard direction in a generally cantilevered manner coaxially surrounding the wheel axle. An end disk at the outboard end of the torque tube is both rotationally and axially fixed to the torque tube. When one or more brake actuators are energized, corresponding pistons force a brake pressure plate to compress the disk stack between the pressure plate and end plate, slowing the vehicle. The non-rotating brake structure typically has strong radial and torsional vibration modes that are concentric with the axle. The vibrations result in passenger annoyance and may cause brake control feedback interference. Extended repetitive vibrations events may cause excessive wear, fatigue, or ultimate structural failure. Additional structural features may be added to reduce vibration, but add to the overall weight of the system. It is desirable to reduce braking system vibrations without adding significantly to the weight of the braking mechanism. It is also desirable to provide a braking system which reduces brake-induced vibration, torque oscillations, hydraulic pressure oscillations, and unnecessary transfer of brake heat to the axle, all at a very modest increase in braking system cost.
Braking systems may exhibit an undesirable whirl vibration during a braking event. The present invention reduces principally whirl-mode vibrations produced by multi-disc brakes leading to structural wear and failure, or brake control feedback interference. The torque tube is a major structural component of the brake. While mounted on the axle, the torque tube has strong radial and torsional vibration modes that are concentric with the axle and the brake discs which energize vibration in surrounding structures. Prior art torque tubes are designed to be symmetric with the axle axis and have an elastic center that lies on that axis. The elastic center is defined as the neutral axis of bending of the structure. The present invention shifts the elastic center of the torque tube to lie off-axis of the brake disks, and imparts vibration mode asymmetry to the torque tube, for example by employing cut outs or material removal at portions of the torque tube that reduce or weaken vibration modes. By purposefully adding asymmetry to the torque tube, its vibration modes are weaker and not concentric with the axle axis or the brake disks. This significantly reduces the amplitude and duration of brake-induced vibration.
The invention comprises, in one form thereof, a torque tube for angularly fixing alternate disks in a multi-disk brake assembly and limiting axial movement of the alternate disks as well as the intervening disks in the form of a hollow generally annular member having an axis, a radially outwardly flared portion near one end to facilitate axially fixing an end one of the disks, a flange near the other end thereof adapted to fix the torque tube to a stationary member, and a radially inwardly extending annular support flange disposed intermediate the one and other ends for augmenting the support of the tube on the stationary member. The torque tube elastic center is displaced from the axis and the torque tube exhibits asymmetric stiffness.
An advantage of the present invention is that adverse vibration associated with the torque tube is reduced or avoided without increasing the torque tube mass. Also, conductive transfer of brake heat to the axle is reduced.